1. Field of the Invention
This invention relates generally to a compact fluorescent lamp, and more particularly to such a lamp having a winding envelope and an incandescent lamp base.
2. Description of Prior Art
Fluorescent lamps have been used as a general source of illumination for many years. A fluorescent lamp has high lighting efficiency and a low consumption of electric power in comparison with an incandescent lamp and therefore a compact fluorescent lamp provided on an incandescent lamp base, i.e. an E 26-type screw base, has been developed. But in order to interchange an incandescent lamp with such a compact fluorescent lamp, it is necessary for the fluorescent lamp to have a folded envelope because, in order to obtain about the same brightness as with an incandescent lamp, it is necessary for the fluorescent lamp's envelope to have a certain minimum length. Such a compact fluorescent lamp is known, for example, from U.S. Pat. Nos. 3,953,761 and 4,199,708. Such a fluorescent lamp has a lamp base providing a plurality of screw thread portions, a screw base which is secured to the thread portions of the lamp base, a globe, a partition plate dividing the base side and the globe side, a winding envelope and a ballast provided to the partition plate, in which screw threads are formed on both the lamp base and the screw base itself. However, as the screw base is mounted directly to the lamp base in a conventional lamp, it is necessary for the lamp base to be subjected not only to a torsion moment when attaching to a socket but also to the total weight of the lamp including a heavy ballast, a winding envelope and other equipment attached by way of the partion plate.
Moreover, in such a compact fluorescent lamp, the winding envelope and the ballast are disposed close together and are encased inside the base and the globe. Consequently, the temperature of the winding envelope rises on account of the radiant heat of the ballast and the hot air inside the base and the globe. When the winding envelope reaches a high temperature, the vapor pressure of the mercury sealed in the envelope exceeds the optimum vapor pressure. As a result, the strength of ultraviolet rays emitted in the envelope decreases, so that the lighting efficiency of the fluorescent lamp falls.